Abstract: Crude sodium hexafluorosilicate containing gypsum as a principal impurity can be refined economically with a minimized loss of fluorine by first making the crude fluorosilicate in the form of an aqueous slurry react with an alkali metal compound such as sodium carbonate or sodium hydroxide to form a soluble sulfate, and then treating the solid component of the reaction product with an acid solution in the presence of sodium ion, preferably at elevated temperatures near boiling point, to form a soluble calcium salt and crystallize sodium hexafluorosilicate. Sea water may be used both as the aqueous medium for the slurry in the first step and as the source of the sodium ions in the second step.

Abstract: Ammonium tetrafluoroaluminate particles having an average particle size above 50.mu. are reacted with an aluminum compound such as aluminum hydroxide or oxide first at a temperature of 250.degree. C to 300.degree. C and then at a temperature of 350.degree. to 500.degree. C to form crystalline particles of anhydrous aluminum fluoride (II) with an average particle size almost corresponding to the starting ammonium tetrafluoroaluminate. The heating of the crystalline particles to a temperature above 550.degree. C results in formation of aluminum fluoride (I) with a large average particle size.

Abstract: A process for producing sodium fluoride from sodium silicofluoride in which sodium silicofluoride is added to an ammonium fluoride solution for double decomposition reaction to obtain a slurry containing sodium fluoride as crystals and ammonium silicofluoride in dissolved form, and the solution from which the sodium fluoride crystals have been removed is added with ammonia to decompose the ammonium silicofluoride into silica and ammonium fluoride. The ammonium fluoride obtained by the decomposition is recycled to the double decomposition step. Alternatively, the ammonium fluoride is reacted with a sodium salt for recovery as sodium fluoride.

Abstract: An aqueous slurry of CaHPO.sub.4.2H.sub.2 O in a 5-20 Wt% concentration is prepared by the use of the phosphate dihydrate obtained by reaction of NaNH.sub.4 HPO.sub.4.4H.sub.2 O with CaCl.sub.2 in water. After adjustment of the pH of the slurry to 4.5-5.5, the slurry is rapidly heated to 85.degree.-97.degree. C by contact with steam to convert the dihydrate to the anhydride, which is suitable for use in the preparation of fluorescent materials due to its high purity, platy and square crystal shape and uniform particle size.